1. Technical Field
The present invention relates generally to an energy recovery device for a desalination system and, more particularly, to a self-reciprocating energy recovery device utilized in driving of a seawater pump by self-reciprocating a piston of a power recovery chamber and recovering energy not using an electronic drive unit but using the hydraulic power of concentrated water.
2. Description of the Related Art
In general, in order to acquire freshwater from seawater, substances dissolved or floating in seawater need to be removed to satisfy the standards for water and drinking water. Desalination methods mainly include reverse osmosis and electric dialysis using special membranes, and evaporation for changing seawater into vapor to desalinate seawater, and also may use freezing and solar heat.
A desalination plant using electric dialysis uses semi-permeable membranes that entirely exclude ion materials dissolved in water and pass pure water to filter ionic materials dissolved in seawater.
A process using high pressure above standard osmosis pressure is needed to separate ionic materials and pure water from seawater is referred to reverse osmosis, and a high pressure of 42 to 70 bars is needed in desalination of seawater.
The operation of the desalination system using reverse osmosis is as follows.
First, the seawater introduced from the sea is supplied through a low-pressure pump for reverse osmosis via a pre-treatment process.
Some of the seawater supplied through the low-pressure pump is supplied to a membrane after being pressurized by a high-pressure pump, and some of the seawater supplied to the membrane is discharged to treated water from which salt is removed by reverse osmosis and the remainder is supplied to an energy recovery device as high-pressure concentrated water.
The energy recovery device includes a pair of power recovery chambers recovering hydraulic power of concentrated water, a plurality of check valves for interrupting the seawater supplied to the power recovery chambers, and an electric actuator drive spool valve for controlling pistons inside the power recovery chambers to alternately reciprocate.
In a simple explanation of the operation of such an energy recovery device, some of the high-pressure seawater that has passed through a high-pressure pump is discharged to treated water from which salt is removed through a membrane and the remainder is provided to the energy recovery device as high-pressure concentrated water.
High-pressure concentrated water is alternately supplied to the power recovery chambers by interrupting the electric actuator drive spool valve. Then, the pistons are moved by the pressure of the high-pressure concentrated water, whereby high-pressure seawater is supplied to a membrane module and low-pressure seawater is selectively supplied to the power recovery chambers through a boost pump by selective opening/closing of a check valve.
In the desalination system using reverse osmosis, the energy recovery device can make the capacities of the low-pressure pump and the high-pressure pump smaller and the power of electric motors driving the low-pressure pump and the high-pressure pump less by recovering the hydraulic power of the concentrated water that has been treated in the membranes, saving energy.
However, such an energy recovery device separately includes a chamber having a cylindrical piston to use hydraulic pressure in reverse osmosis, and a linearly moved spool valve selectively controlling driving of a cylindrical piston in the chamber.
In other words, since the rotational movement of the electric motor needs to be converted to linear movement and the electric actuator drive spool valve such as an electric linear motor and a proportional control valve needs to be provided outside a chamber, the device becomes complex and the size of the device increases.
In order to overcome the above-mentioned disadvantages, the present applicant has disclosed an energy recovery device in Korean Patent Application No. 2008-0054464.
The technology enables reduction of the size of the device, precise control of the device, and linear flow of fluid by using a conventional spool valve selectively supplying concentrated water to a power recovery chamber as a concentrated water control valve block having a fluctuating plate-like concentrated water valve and directly controlling rotation using an electric motor.
However, since the technology uses a separate electric motor for driving a fluctuating plate-like concentrated water valve, power for driving of an electric motor is consumed and a waterproof structure for interrupting contact with water is needed, making the device complex and larger.